Protective coatings on metals



United States This invention relates to protective coatings for metalsand to coating baths and coating methods for applying such protectivecoatings to metals.

Various coatings have been utilized heretofore to protect base metals,i.e., metals which corrode and discolor upon exposure to variousoperating conditions such as high humidity, salt water and the like.These coatings have been applied by many different methods using a largevariety of coating baths and coating methods. It

"has been desirable in certain instances to provide coatings that aretransparent whereby to leave substantially unchanged the color of thesurface coated. On the other hand it is desirable in other instances tocolor the coated surface. I

A particular example of an application in which it is desired to imparta particular color to a metal surface is the use of steel strapping tobind aluminum ingots. It has been customary heretofore to provide agalvanized coating on the steel strapping but it has been found that thecolor of the galvanized steel is confusingly similar to the color of thealuminum ingots, whereby the steel strapping is often thrown into thestorage bins with the aluminum ingots thereby to contaminate thealuminum.

There are disclosed in my co-pending application Serial No. 724,794,filed March 31, 1958 for Protective Coatings on Metals, now Patent No.3,007,818, issued November 7, 196 1, protective coatings, and coatingbaths and methods of applying the coatings, which may be eithersubstantially colorless and transparent or which may be colored in oneof many ways." The invention of this application is an improvement uponthe subject matter of the above application in that better coatings andmore desirable colors can be provided thereby. Accordingly, it is animportant object of the present invention to provide improved protectivecoatings for base metals and to provide improved coating baths andimproved coating methods to apply the protective coatings to the basemetals.

Another object of the invention is to provide an improved coating forbase metals which has a'desirable predetermined color and particularly acolor which contrasts with the color of galvanized coatings andaluminum.

Yet another object of the invention is to provide improved coating bathsand coating methods which produce the colored protective coating of thepresent invention on a'base metal surface inasingle step process.

Still another object of the invention isto provide improved coatings ofthe type set forth which comprise a combination of different coatingcompounds on the metal surface being treated.

A further object of the invention is to provide an improved coating bathand method of applying the coating which can be operated atsubstantially room temperature utilizing simple equipment and simple andinexpensive operating procedures.

It has been found that good protective coatings can be applied to basemetal surfaces by applying thereto a composition containing an anion ofa phosphoric acid ester of cyclohexanol and a compound selected from theclass consisting of zirconium salts and basic zirconium saltsdistributed in a suitable carrier. A preferred class of ester ofcyclohexanol are those which are the anions of a phosphoric acid esterof hexahydroxycyclohexanol (inositol), the preferred anion being that ofinositol hexaatent weight of free phytic acid to-provide a concentrationin 3,076,734 Patented Feb. 5, 1963 phosphoric acid commonly calledphytic acid; the phytic acid may be applied as the free acid or as asalt thereof, the sodium, potassium, cadmium and magnesium salts beingparticularly advantageous. The preferred 'zirconium compound for use inthe present invention is zirconium oxychloride.

A preferred class of carriers useful in the present invention arehydrophilic carriers. For example, aqueous solutions, oil-wateremulsions and wax-like compositions containing water and otherhydrophilic materials can be used satisfactorily. In general any basemetal that will react with an acid medium can be treated successfully toprovide a protective coating thereon using this invention, the pH of theacid medium being from 0.8 to about 6.9.

The concentration in the carrier of the phytic acid or salt thereof usedin the present invention is preferably from about 00001 mol/liter toabout 0.1 mol/liter. The zirconium ion is preferably present in thecarrier in a concentration from about 0.001 mol/liter to about 0.1-mol/liter; it further is desirable that the molar ratio between thezirconium ions and the phytate ions present he in the range from about 1to about 50. It further is desirable in certain instances to providecoatings including a compound derived from chromic acid, dichromic acidand salts thereof in which case the chromate may be present in thecarrier in a concentration of about 0.01 mol/liter to about 1.0mol/liter.

By a proper choice of the composition and concentration of theingredients and by the proper control of the pH, the time required toobtain a satisfactory coating upon application of the coatingcomposition may be from a fraction of a second up to as much as 30minutes or an hour or more.

It also has been found that satisfactory coatings having a desired colorcan be achieved by utilizing a coating composition including an acidichydrophilic carrier having incorporated therein a compound selected fromthe class consisting of zirconium salts and basic zirconium salts and asecond compound selected from the class consistingof chromic acid anddichromic acid and salts thereof. In such compositions the zirconiumcompound is present in a concentration of from about 0.001 mol/liter toabout 0.1 mol/liter and the chromium compound is present in aconcentration from about 0.01 mol/liter to about 1.0 mol/liter, themolar ratio between the chromium and zirconium present being from about0.1 to about 10; the pH is preferably in the range from about 0.8 toabout 6.9 and the time necessary to apply the compositionto obtain asatisfactory coating may be from a fraction of a second up to as much as30 minutes or an hour or more.

It further has been found that the corrosion protection afforded by allof the above compositions can be materially enhanced by incorporatingtherein a compound selected from the class consisting of salts ofarsenic and oxides of arsenic and salts thereof, the arsenic compoundbeing present in a concentration from about 0.001 mol/ liter to about0.05 mol/ liter. The character of the coat ing can also be improved byincorporating in the compositions a cationic fatty amide derivative suchas that sold under the trademark Protamine by the Procter Chemical Co.,the fatty amide preferably being present in an amount from about 0.1 to5 grams per liter.

The following specific examples of protective coatings, coatingcompositions and coating methods illustrate the application of thepresent invention and it is to be undere stood that these examples arenot intended in any way to limit the scope of the present invention.

Example 1 A coating composition was prepared by adding to water anaqueous solution of phytic acid containing 70% by the coating solutionof about 5 grams per liter of phytic acid. Sufiicient zirconiumoxychloride octahydrate was added to provide a concentration thereof inthe coating solution of about 5 grams 'per liter. The pH was thenadjusted to 1.4 by adding concentrated nitric acid. A cleaned strip ofgalvanized mild carbon steel was provided and immersed in the coatingsolution for seconds toform a'coating thereon. The coated strip was thentaken from thesolution and any excess coating solution removed. Afterdrying, the coated steel strip was examined and found to have a brownprotective coating of phytate and zirconium thereon. The coatingprovided good protection against humidity and salt water when subjectedto humidity and salt water corrosion tests. The strip prepared exhibitedbetter corrosion properties than a like strip having only a phytateprotective coating thereon.

' The method of Example 1 above has been operated successfully when theconcentration of the phytic acid in the coating solution has beenincreased to as much as 25 grams per liter or more and smallerconcentrations of phytic acid can also be used but there results acoating which is much lighter in weight. The zirconium oxychloride hasalso been successfully increased to as much as 30 grams. per liter anddecreased to as little as 0.3 gram per liter while'still providing asatisfactory color in the coating, it' being understood that the morezirconium oxychloride present the darker is the color of the resultantcoating for like times of exposure. It further was found that the pH 'ofthe coating solution could be varied from approximately 1.0 toapproximately 2.0 and still provide satisfactory coatings with the sameexposure.

Example 2 The coating solution and method described above in Example 1with respect to a. zinc surface were applied to a cadmium surface. Aprotective coating was formed on cadmium which had a desirable browncolor and which provided good protection against corrosion by humidityand salt water.

Example 3 A mild carbon steel strip was provided and the coatingsolution and method described above in Example lwer'e applied thereto. Aprotective coating having a desired light brown color was obtained, the.coating providing good protection against corrosion by humidity and saltwater. 7

Iri'general, any of the base metals that react with acidic mediums orsolutions can be coated using the coating solution and method of Example1, 'tin and copper being other specific. examples of metals on which thesolution and methodof Example 1 have been successfully employed; Thecoating solution may contain, for exam ple, from about'0.000lmol/literof-phytate ion (empirical rdr'mfila'c n so r y to' about 0:1moi/liter. and from about. 0.001 mol/liter to about 0.1 mol/liter ofzirconium ion. When such concentrations'are used in an acid solution,the immersion time will be in the order. of- 10 to 20 seconds toprovide. an'adequate. protective phytate and zirconium containingcoating. In general, if the concentration of phytate and zirconiumcontaining ions is lower, the amount of coating laid down during a givenof time will be less. Conversely, if the concentration of phytate ion.and zirconium containing ion is increased, a heavier coating 'will beformed on the metal duringfa given period of time. The amount of coatinglaid down during a given period of time is less if the pH is higherv andis greater if the pH is lower. Those skilled in theart. will be able toascertain satisfactory conditions forlaying down the desired weight. ofcoating from the above examples. i i

It has been found that it is also possible to co-deposit a chro matecoating. on the base metal with the phytate and zirconium coatingobtained by the coating solution aud method of Example 1. The followingis an example of a suitable coating solution and method for producing acombination coating including a chromate therein.

Example 4 The following ingredients were mixed to provide a liter ofcoating solution having the concentrations indicated.

Grams/liter Sodium dichromate (Na Cr O -2H O) 10 Zirconium oxychloride(ZrOC1 -8H O) 5 Sodium phytate l The solution had the pH thereofadjusted to 1.4 and was heated to F. A galvanized steel strip was coatedby immersing it for 10 seconds in the heated solution. The resultantcoating had good adhesion, was light brown in color, and provided goodcorrosion resistance to both high humidity and salt water.

Other sources of chromium may be used instead of the sodium dichromateset forth in Example 4, i.e., chromic acid, dichromic acid, and othersalts thereof, such, for example, as potassium dichromate can be used inplace of sodium dichromate. The following is an example of the use ofchromic acid as a source of chr0- mium:

Example 5 The following ingredients Were mixed in a liter of water toprovide the concentrations indicated:

Grams/liter Chromic acid (CrO 6 Zirconium oxychloride (ZrOC1 -8H O) 10Sodium phytate 2 The pH of this coating solution was adjusted to 1.4. Aclean galvanized strip of steel was provided and was coated by dippingit in the solution at room temperature, i.e., about 75 F. A 10 secondimmersion produced a brown coating, and a 20 second immersion produced abrownish green coating. Both coatings exhibited good adhesion and gavegood protection against high humidity and salt water. The solutions andmethods of Examples 4 and 5 have also been applied successfully to tinand copper surfaces.

The following is an example of a production coating bath useful incoating galvanized steel strapping to provide thereon a combinationcoating including phytate, a zirconium compound and chromate.

Example 6 To 10 gallons of water were added 46.75 pounds of sodiumdichromate, the solution being stirred until all of the sodiumdichromate was dissolved. Nitric acid (70% solution in water by. weight)was then added in the amount of 4.0 gallons (15.16 liters). 10 pounds ofzirconium oxychloride octahydrate were then added after which the volumeof the solution was brought to 20 gallons by the addition of water. Thissolution was then stirred until all materials were completely dissolvedwhereby to provide a concentrate which can be subsequently diluted toprovide the production coating solution. The production coating solutionwas prepared from the concentrate by diluting it 1:20 so that the 20gallons of concentrate provided 400 gallons of solution to which wasadded 2.0 gallons (7.58 liters) of an aqueous solution of phytic acid.containing 70% by weight of phytic acid. The production coating solutioncontained the following concentrations of active ingredients.

Phytic acid 7.2 gms./l. (0.011 moi/liter). Zirconium oxychloride 3gms./l. (0.00932 mol/liter). Sodium dichromate 14 gms./l. (0.047mol/liter).

The coating solution will have a pH of 0.9 and the pH is maintainedduring operation in the range 0.9 to 1.3. The operating temperature ofthe coating solution is maintained at F.;+:5 F.

As an example of the use of the production coating solution, it was usedin coating a galvanized steel strip having a width of 2 inches and athickness of 0.011 inch which was galvanized on both sides to athickness of 0.00004 inch. The galvanized strip was run through theheated coating solution in a continuous manner and each portion of thestrip Was immersed in the coating bath for a period of from 9 to 13seconds. There was produced on the strip an attractive brown coatinghaving good adhesion and providing good protection against corrosion byhigh humidity and saltwater.

The zirconium concentration in the bath must be maintained atsubstantially the above stated level by substantially continuousreplenishment and the control of the rate of addition of zirconium ioncan be accomplished by watching the color of the coated strip, since thecolor is a good indication of the amount of zirconium ion present in thecoating bath. The other constituents of the coating solution may bedepleted by as much as 25% before replacement is required. Theconcentrate solution may be used to accomplish replacement but often thedrag-out will be sufiicient so that the lost Solution must be replacedin an amount that will compensate substantially for the depletion of theactive ingredients from the coating solution by deposition thereof onthe galvanized strip. The coating solution must be discarded andreplaced 'when the zinc concentration therein reaches 12 grams perliter.

The production run set forth in Example 6 above was successfullyrepeated using 1.5 grams per liter of zirconium oxychloride and 5 gramsper liter of zirconium oxychloride in the coating bath. The coatingsobtained therefrom possessed all of the desirable characteristics setforth above with respect to the coating obtained from Example 6, theonly difference being in the color of the coating produced, the lowerconcentration providing a coating having a light brown color with aslight greenish tint and the higher concentration providing a coatinghaving a golden brown or dark brown color.

Chromic acid and phytic acid may be utilized as in gredients in the samebaths. The following is an example of the use of these ingredients.

Example 7 The following ingredientswere placed in a liter of water toprovide .the indicated concentrations:

Grams per liter The pH of the solution was adjusted to 1.4 usingconcentrated nitric acid. A galvanized steel strip was coated byimmersing the strip in the solution for 10 seconds at 120 F., and therewas produced thereon a deep brown protective coating which had goodadhesion and excellent resistance to corrosion by high humidity and saltwater.

It was further found that the coating produced could be improved as toadhesion and corrosion resistance by addingthereto cationic fatty amidederivatives of the type sold under the trademark Protamine by theProcter Chemical Co} The following is an example of such a coatingsolution.

A galvanized strip was coated using the above solution by immersing thestrip for 10 seconds in the solution at room temperature, i.e., 75 F.The coating thus produced was adherent, had a brown color and gave goodcorrosion resistance againsthigh humidity and salt water. The coatingwas analyzed spectrographically and it was de- The following ingredientswere added to water to provide the concentrations indicated:

Grams per liter Chromic acid (*CrO 4.8 Zirconium oxychloride (ZrOCI -SHO) 5 Sufficient nitric acid was added to reduce the pH to 1.4,approximately 10 cc. of concentrated nitric acid being required perliter of coating solution. A galvanized steel strip was coated byimmersing the strip for 10 seconds in the coating solution at atemperature of 120 F. The resultant coating was a deep reddish brown,possessed adevquate adhesion and provided excellent corrosion resistanceagainst high humidity and salt water.

The coating solution of Example 9 above can be prepared by substitutingsodium dichromate for the chromic acid and by providing a much greaterconcentration of zirconium oxychloride as follows.

Example 10 These ingredients were added to water to provide theconcentrations indicated: Grams per liter Sodium dichromate 50 Zirconiumoxychloride 50 The pH of the sodium solution was 1.0. A galvanized steelstrip was coated with this solution by immersing it in the solution at atemperature of 100 F. There resulted a protective coating having a deepbrown'color. The solutions and methods of Examples 9 and 10 have alsobeen used to provide protective coatings on tin and copper.

Even better corrosion resistance can be obtained from the coatings ofthe present invention if the coating solutions have added thereto asmall amount of arsenic, for example, arsenic pentoxide (As O Thefollowing is an example of a bath incorporating arsenic therein.

Example 11 The following ingredients were added to water to provide theconcentrations indicated:

Grams per liter Phytic acid 5 Zirconium oxychloride (ZrOCl -8H O) 5Arsenic pentoxide (As O 5 'did the coating obtained by Example 1.

Arsenic can also be added advantageously to those coating solutions inwhich chromium is one of the active constituents. The following is anexample using such a solution.

Example 12 The following ingredients were added to water to provide theconcentrations indicated:

' Grams per liter Sodium dichromate (N21 Cr O -2H O) 14 Zirconiumoxychloride (ZrCI -SH O) 3 Arsenic pentoxide (As O 5 Phytic acid 7 ThepH of this solution was adjusted to 1.4 by the addition of concentratednitric acid. A galvanized steel strip was coated by immersing the stripfor 10 seconds in the solution at 120 F. The resultant coating was veryadherent and provided excellent corrosion resistance against humidityand salt water. Higher concentrations of the arsenic pentoxide providedslightly less corrosion protection and lower concentrations of thearsenic pentoxide likewise provided less corrosion protection than theoptimum value of grams per liter set forth in Example 12. However, allof the coatings formed using arsenic pentoxide as an ingredient in thecoating solution showed improved corrosion protection over thosecoatings provided by identical solutions but omitting the arsenicpentoxide therefrom.

Arsenic is also useful in those coating compositions which include onlysources of chromium and zirconium as the active constituents. Thefollowing is an example of such a coating composition.

Example 13 The following ingredients were added to water to provide theconcentrations indicated:

Grams per liter Chromic acid (CrO' 4.8 Zirconium oxychloride (ZrOCl '8HO) 4.8 Arsenic pentoxide (As O 5 The pH of this solution was adjusted to1.4 by the addition of approximately cc. of concentrated nitric acid perliter of solution. A galvanized steel strip was coated utilizing thesolution of Example 13 and the resultant coating exhibited goodadhesion, provided good corrosion protection and had a distinctive browncolor.

The ingredients utilized in Example 6 above can also be incorporated ina hydrophilic wax-like base which can be used to provide a protectiveCoating on aluminum surfaces. The following is an example of theapplication of the principles of the present invention in this manner.

Example 14 The following ingredients were mixed in the proportionsindicated:

Gms. Cetyl alcohol 7 Stearyl alcohol 3 White. beeswax 4 Petrolatum 27Glycerine 8 In a separate container the following materials were mixedin the proportions indicated:

' Gms. Sodium lauryl sulfate (saponifying agent) 1 Distilled water 50Zephiran chloride (a germicide and preservative comprising a mixture ofalkyldimethylbenzylammonium chlorides) 0.06

A quantity of the coating solution of Example 6 was treated to evaporatethe major portion of the water therefrom whereby to form a paste. 25gms. of the paste so formed were mixed together with the materials setforth above including the hydrophilic base, the saponifying agent andthe preservative. The resultant mixture has a pH in the range 2.5 to2.8. This coating composition was applied to aluminum by spreading alayer thereof on the aluminum surface to be protected. The coating wasleft in position for about 30 minutes and then wiped off. It was foundthat a protective coating had been formed on the aluminum surface whichwas highly resistant to corrosion as determined by humidity and saltwater exposure tests.

Instead of using the solution of Example 6, compositions for coatingaluminum have also been prepared by forming pastes from the solutions ofExamples 1 to 5 and 7 to 13 and incorporating those pastes in thehydrophilic base of Example 14.

The phytic acid utilized in certain of the above examples was specifiedto be an aqueous solution containing approximately 70% by weight ofphytic acid in a relatively pure state. It has been found that it is notnecessary to use substantially pure phytic acid and, in fact, wastesolutions called steep liquor resulting from the steeping of grain aresufficiently rich in phytic acid to work satisfactorily. These liquorscontain about 10% to 30% of phytic acid by weight. The other impuritiesfound therein also do not interfere with the coating action. The sodiumphytate specified in certain of the examples is prepared by addingconcentrated sodium hydroxide solution to a 70% by weight aqueoussolution of phytic acid until the pH thereof is approximately 4.7. Theconcentration of the phytate ion in solutions made in accordance withthe present invention may be in the range from about 0.0001 mol/liter to0.1 mol/liter, a preferred range being 0.001 mol/ liter to about 0.05mol/ liter. It is believed that the coatings formed on metal surfacesfrom solutions including the phytate ion contain as one of theconstituents thereof a phytate compound of the metal of the surface,i.e., zinc surfaces including zinc phytate, steel surfaces includingiron phytate, cadmium surfaces including cadmium phytate, tin surfacesincluding tin phytate, copper surfaces including copper phytate,aluminum surfaces containing aluminum phytate, etc.

In general, the zirconium in the coating compounds can be derived fromany zirconium salt soluble in acidic aqueous media but preferably fromthe basic zirconium salts such as zirconium oxychloride. Other examplesof sources of zirconium are zirconium ammonium fluoride, zirconiumtetrachloride, zirconium nitrate, zirconium potassium fluoride andzirconium sulfate. The concentration of zirconium ion in the coatingcomposition may be from 0.001 mol/liter toabout.0.1 mol/liter butpreferably is in the range 0.003 to about 0.03 mol/ liter. It isbelieved that the zirconium in the coating formed on the metal surfaceis present as the corresponding zirconate (ZrO of the metal surface,i.e., zinc surfaces including in the coating zinc zirconate, steelsurfaces including iron zirconate, cadmium surfaces including cadmiumzirconate, aluminum surfaces including aluminum zirconate, tin surfacesincluding. tin zirconate, copper surfaces including copper zirconate,etc.

The chromium present in certain of the coating solutions may be derivedfrom chromic acid, dichromic acid or salts thereof such as sodiumdichromate, potassium dichromate, etc. The concentration of the chromiumin the coating composition may be from about 0.01 mol/liter to about 1.0mol/liter. It is believed that the coatings formed on metal surfacesfrom solutions including the chromate ion contain as one of theconstituents thereof a chromate compound of the metal of the surface,i.e., zinc surfaces including zinc chromate, steel surfaces includingiron chromate, cadmium surfaces including cadmium chromate, tin surfacesincluding tin chromate, copper surfaces including copper chromate,aluminum surfaces containing aluminum chromate, etc.

It further has been found that it is desirable in those compositionsincluding both phytate ions and chromium that the molar ratio ofchromium to phytate be from about 1 to about 50. In those compositionsincluding both zirconium and chromium, it is preferred that the ratio ofzirconium to chromium be about 0.1 to about 10. Further, in thosecompositions including both zirconium and phytate it is preferred thatthe ratio of zirconium to phytate be from about 1 to about 100.

The arsenic present in certain of the above examples may be derived fromany of the salts of arsenic, from the oxides thereof or the saltsthereof which are soluble in acidic aqueous media, the preferred sourcebeing arsenic pentoxide. Other suitable sources are ammonium dihydrogenorthoarsenate, potassium orthoarsenate, potassium 9 monohydrogenorthoarsenate, potassium dihydrogen orthoarsenate, sodium orthoarsenate,sodium monohydrogen orthoarsenate (both the heptahydrate and thedodecahydrate) sodium dihydrogen arsenate, and potassium arsenite. Thepreferred concentration of arsenic in the coating composition is fromabout 0.001 mol/liter to about 0.05 mol/liter.

Although certain preferred examples of the invention have been given forpurposes of illustration, it is to be understood that various changesand modifications can be made thereon Without departing from the spiritand scope of the invention and it is intended to cover in the followingclaims all such changes and modifications that fall within the scopethereof.

I claim:

1. A composition for use in providing a protective coating on basemetals consisting essentially of a first compound selected from theclass consisting of phytic acid and salts thereof and ayseco-nd compoundselected from the class consisting of acid soluble zirconium salts andbasic zirconium salts, said first and second compounds being present inamounts equivalent to from about 0.0001 to about 0.1 mole of said firstcompound and from about 0.001 to about 0.1 mole of said second compound,the molar ratio of said second compound to said first compound being inthe range from about 1 to about 50.

. 2. A composition for use in providing a protective coating on basemetals consisting essentially of a first compound selected from theclass consisting of phytic acid and salts thereof, a second compoundselected from the class consisting of acid soluble zirconium salts andbasic zirconium salts, and a third compound selected from the classconsisting of chromic acid, dichromic acid and salts thereof, saidcompounds being present in amounts equivalent to from about 0.0001 toabout 0.1 mole of said first compound and from about 0.001 to about 0.1mole of said second compound and from about 0.01 to about 1.0 mole ofsaid third compound, the molar ratio of said second compound to saidfirst compound being in the range from about 1 to about 50, the molarratio of said third compound to said second compound being in the rangefrom about 0.1 to about 10.

3. A composition for use in providing a protective coating on basemetals consisting essentially of a first compound selected from theclass consisting of phytic acid and salts thereof, a second compoundselected from the class consisting of acid soluble zirconium salts andbasic zirconium salts, and a third compound selected from the classconsisting of acid soluble salts of arsenic, oxides of arsenic and saltsthereof, said compounds being present in amounts equivalent to fromabout 0.0001 to about 0.1 mole of said first compound and from about0.001 to about 0.1 mole of said second compound and from about 0.001 toabout 0.05 mole of saidthird compound, the

molar ratio of said second compound to said first compound being in therange from about 1 to about 50, the molar ratio of said first compoundto said third compound being in the range from about 1 to about 100.

4. A composition for use in providing a protective coating on basemetals consisting essentially of a first compound selected from theclass consisting of phytic acid and salts thereof, a second compoundselected from the class consisting of acid soluble zirconium salts andbasic zirconium salts, ,a third compound selected from the classconsisting of chromic acid and dichromic acid and salts thereof, and afourth compound selected from the class consisting of acid soluble saltsof arsenic, oxides of arsenic and salts thereof, said compounds beingpresent in amounts equivalent to from about 0.0001 to about 0.1 mole'ofsaid first compound and from about 0.001 to about 0.1 mole of saidsecond compound and from about 0.01 to about 1.0 mole of said thirdcompound and from about 0.001 to about 0.05 mole of said fourthcompound, the molar ratio of said second compound to said first compoundbeing in the range from about 1 to about 50,

the molar ratio of said third compound to said second compound being inthe range from about 0.1 to about 10, and the molar ratio of said firstcompound to said fourth compound being in the range from about 1 toabout 100.

5. A coating composition to provide a protective coating on base metalsconsisting essentially of an aqueous solution having a pH in the rangefrom about 0.8 to about 6.9 and containing from about 0.0001 to about0.1 mole per liter of phytate ion and from about 0.001 to about 0.1 moleper liter of a compound selected from the group consisting of acidsoluble zirconium salts and basic zirconium salts.

6. A coating composition to provide a protective coating on base metalsconsisting essentially of an aqueous solution having a pH in the rangefrom about 0.8 to about 6.9 containing from about 0.0001 to about 0.1mole per liter of phytate ion, from about 0.001 to about 0.1 mole perliter of a compound selected from the group consisting of acid solublezirconium salts and basic zirconium salts, and from about 0.01 to about1.0 mole per liter of a compound selected from the group consisting ofchromic acid and dichr-omic acid and salts thereof.

7. A coating composition to provide a protective coating on base metalsconsisting essentially of an aqueous solution having a pH in the rangefrom about 0.8 to about 6.9 containing from about 0.0001 to about 0.1mole per liter of phytate ion, from about 0.001 to about 0.1 mole perliter of a compound selected from the group consisting of acid solublezirconium salts and basic zirconium salts, and from about 0.001 to about0.05 mole per liter of a compound selected from the class consisting ofacid soluble salts of arsenic, oxides of arsenic and salts thereof.

8. A coating composition to provide a protective coating on base metalsconsisting essentially of an aqueoussolution having a pH in the rangefrom about 0.8 to about 6.9 containing from about 0.0001 to about 0.1mole per liter of phytate ion, from about 0.001 to about 0.1 mole perliter of a compound selected from the group consisting of acid solublezirconium salts and basic zirconium salts, from about 0.01 to about 1.0mole per liter of a compound selected from the class consisting ofchromic acid and dichromic acid and salts thereof, and from about 0.001to about 0.05 mole per liter of a compound selected from the classconsisting of salts of arsenic, oxides of arsenic and salts thereof.

9. A coating composition to provide a protective coating on base metalsconsisting essentially of an aqueous solution having a pH in the rangefrom about 0.8 to about 6.9 and containing from about 0.001 to about0.05 mol/ liter of phytate ion, from about 0.003 to about 0.03 mol/liter of a compound selected from the group consisting of acid solublezirconium salts and basic zirconium salts and from about 0.01 to about1.0 mol/liter of chromate ion.

10. A coating composition to provide a protective coating on base metalsconsisting essentially of an aqueous solution having a pH in the rangefrom about 0.8 to about 6.9 and containing from about 0.001 to about0.05 mol/ liter of phytate ion, from about 0.003 to about 0.03 mol/liter of a compound selected from the group consisting of acid solublezirconium salts and basiczirconium salts, from about 0.01 to about 1.0moi/liter of chromate ion, and from about 0.001 to about 0.05 moi/literof a compound selected from the class consisting of acid soluble saltsof arsenic and oxides of arsenic and salts thereof.

11. A coating composition to provide a protective coating on base metalsconsisting essentially of an aqueous solution having a pH of about 1.4and containing about 0.01 mol/liter of phytate ion, about 0.01 mol/literof zirconium oxychloride and about0t5 incl/liter of dichromate ion.

12. A coating composition to provide a protective coating on base metalsconsisting essentially of an aqueous conium oxychloride, about 0.05mol/liter of dichromate ion, and about 0.02 mol/liter of arsenicpentoxide.

13. The method of providing a protective coating on base metalscomprising immersing the base metal in a coating composition comprisingan acidic aqueous solution containing from about 0.0001 to about 0.1mole per liter of phytate ion and from about 0.001 to about 0.1 mole perliter of a compound selected from the group consisting of acid solublezirconium salts and basic zirconium salts.

14. The method of providing a protective coating on base metalscomprising immersing the base metal in a coating composition comprisingan acidic aqueous solution containing from about 0.0001 to about 0.1mole per liter of phytate ion, from about 0.001 to about 0.1 mole perliter of a compound selected from the group consisting of acid solublezirconium salts and basic zirconium salts, and from about 0.01 to about1.0 mole per liter of acompound selected from the class consisting ofchromic acid and dichromic acid and salts thereof.

15. The method of providing a protective coating on base metalscomprising immersing the base metal in a coating composition comprisingan acidic aqueous solution containing from about 0.0001 to about 0.1mole per liter of phytate ion, from about 0.001 to about 0.1 mole perliter of a compound selected from the group consisting of acid solublezirconium salts and basic zirconium salts, from about 0.01 to about 1.0mole per liter of a compound selected from the class consisting ofchromic acid and dichromic acid and salts thereof, and from about 0.001to about 0.05 mole per liter of a compound selected from the classconsisting of acid soluble salts of arsenic and oxides of arsenic andsalts thereof.

16. The method of providing a protective coating on base metalscomprising immersing the base metal in a coatingcomposition comprisingan acidic aqueous solution containing from about 0.0001 to about 0.1mole per liter of phytate ion, from about 0.001 to about 0.1 mole perliter of a compound selected from the group consisting of acid solublezirconium salts and basic zirconium salts, and from about 0.001 to about0.05 mole per liter of a compound selected from the class consisting ofacid soluble salts of arsenic and oxides of arsenic and salts thereof.

17. The method of providing a protective coating on base metalscomprising applying to the base metal a coating composition comprisingan aqueous solution containing from about 0.001 to about 0.05 mol/literof phytate ion, from about 0.003 to about 0.03 mol/liter of a compoundselected from the group consisting of acid soluble zirconium salts andbasic zirconium salts, and from about. 0.01 to about 1.0 mol/liter ofdichromate ion, said composition having a pH in the range from about 0.8to about 6.9.

18. The method of providing a protective coating on base metalscomprising applying to the base metal a coating composition comprisingan aqueous solution containing from about 0.001 to about 0.05 mol/literof phytate ion, from about 0.003 to about 0.03 mol/liter of a compoundselected from the group consisting of acid soluble zirconium salts andbasic zirconium salts, from about 0.01 to about 1.0 mol/liter ofdichromate ion, and from about 0.001 to about 0.05 mol/liter of acompound selected from the class consisting of acid soluble salts ofarsenic and oxides of arsenic and salts thereof, said composition havinga pH in the range from about 0.8 to about 6.9.

19. The method of coating galvanized and cadmium plated steel stripswhich. consists in immersing the strip in an acidic aqueous solutioncontaining from about 0.0001 to about 0.1 mole per liter of phytate ion,from about 0.001 to about 0.1 mole per liter of a compound selected fromthe group consisting of acid soluble zirconium salts and basic zirconiumsalts and a mineral acid.

20. The method of coating galvanized and cadmium plated steel stripswhich consists in immersing the strip in an acidic aqueous solutioncontaining from about 0.0001 to about 0.1 mole per liter of phytate ion,from about 0.001 to about 0.1 mole per liter of a compound selected fromthe group consisting of acid soluble zirconium salts and basic zirconiumsalts, and from about 0.001 to about 0.05 moles per liter of a compoundselected from the class consisting of acid soluble salts of arsenic andoxides of arsenic and salts thereof, and a mineral acid.

21. A base metal containing a metal selected from the group consistingof aluminum, cadmium, copper, iron, tin and zinc and having a protectivecoating thereon comprising a phytate compound of the base metal and acompound of the base metal with an ion consisting of atoms selected fromthe group consisting of zirconium and oxygen.

22. A base metal containing a metal selected from the group consistingof aluminum, cadmium, copper, iron, tin and zinc and having a protectivecoating thereon comprising a phytate compound of the base metal, acompound of the base metal With an anion consisting of chromium andoxygen, and a compound of the base metal with an ion consisting of atomsselected from the group consisting of zirconium and oxygen.

23. A base metal containing a metal selected from the group consistingof aluminum, cadmium, copper, iron, tin and zinc and having a protectivecoating thereon comprising a phytate compound of the base metal, acompound of the base metal with an anion consisting of chromium andoxygen, and a compound of the base metal with an ion consisting of atomsselected from the group consisting or zirconium and oxygen, the ratiobetween the chromium and zirconium in said coating being approximately 2to 1 by weight.

24. A zinc containing metal member having a coating comprising zincphytate and a compound of zinc with an ion consisting of atoms selectedfrom the group consisting of zirconium and oxygen.

25. A zinc containing metal member having a coating comprising zincphytate, zinc chromate, and a compound of zinc with an ion consisting ofatoms selected from the group consisting of zirconium and oxygen.

26. An aluminum containing metal member having a coating comprisingaluminum phytate and a compound of aluminum with an ion consisting ofatoms selected from the group consisting of zirconium and oxygen.

27. An aluminum containing metal member having a coating comprisingaluminum phytate, aluminum chromate, and a compound of aluminum with anion consisting of atoms selected from the group consisting of zirconiumand oxygen.

28. An iron containing metal member having a coating comprising ironphytate and a compound of iron with an ion consisting of atoms selectedfrom the group consisting of zirconium and oxygen.

29. An iron containnig metal member having a coating comprising ironphytate, iron chromate, and a compound of iron with an ion consisting ofatoms selected from the group consisting of zirconium and oxygen.

30. A tin containing metal member having a coating comprising tinphytate and a compound of tin with an ion consisting of atoms selectedfrom the group consisting of zirconium and oxygen.

31. A tin containing metal member having a coating comprising tinphytate, tin chromate, and a compound of tin with an ion consisting ofatoms selected from the group consisting of zirconium and oxygen.

32. A copper containing metal member having a coating comprising copperphytate and a compound of copper with an ion consisting of atomsselected from the group consisting of zirconium and oxygen.

33. A copper containing metal member having a coating comprising copperphytate, copper chromate, and a compound of copper with an ionconsisting of atoms selected from the group consisting of zirconium andoxygen.

References Cited in the file of this patent UNITED STATES PATENTSSch-amberger June 6, 1939

13. THE METHOD OF PROVIDING A PROTECTIVE COATING ON BASE METALSCOMPRISING IMMERSING THE BASE METAL IN A COATING COMPOSITION COMPRISINGAN ACIDIC AQUEOUS SOLUTION CONTAINING FROM ABOUT 0.001 TO ABOUT 0.1 MOLEPER LITER OF PHYTATE ION AND FROM ABOUT 0.0001 TO ABOUT 0.1 MOLE PERLITER OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF ACID SOLUBLEZIRCONIUM SALTS AND BASIC ZIRCONIUM SALTS.